A computer network is a collection of interconnected computing devices that exchange data and share resources. In a packet-based network the computing devices communicate data by dividing the data into small blocks called packets. Certain devices within the network, such as routers and switches, maintain routing and/or forwarding information that describe paths through the network. In this way, the packets may be individually transmitted across the network from a source device to a destination device. The destination device extracts the data from the packets and assembles the data into its original form. Dividing the data into packets enables the source device to resend only those individual packets that may be lost during transmission.
A private network may include a number of devices, such as computers, owned or administered by a single enterprise. These devices may be grouped into a number of site networks, and these sites may be geographically distributed over a wide area. As one example, each site network may include one or more local area networks (LANs) connecting the devices at the particular site. In Virtual Private LAN Service (VPLS), provider edge (PE) devices of a service provider network or public network, such as the Internet, may provide a logical interconnect such that customer edge (CE) devices of the site networks belonging to a specific VPLS instance appear to be connected by a single LAN. In order to emulate the single LAN over the public network, the PE devices operate as switches and establish full mesh connectivity with other PE devices associated with the specific VPLS instance. In this case, the PE devices treat multicast traffic as broadcast traffic and flood the multicast traffic to every port associated with the VPLS instance.
In some cases, the CE devices included in the may use protocol independent multicast (PIM) as a multicast routing protocol to transmit multicast traffic from sources to receivers for particular multicast groups within the network sites. The CE devices communicate using PIM Hello messages and PIM control messages, including join requests and prune requests, for multicast groups in order to build a multicast tree for the VPLS instance. In VPLS, the PIM messages between the CE devices are forwarded across the public network by the PE devices. Specifically, the PE devices flood the PIM control messages on all ports of the PE devices associated with the VPLS instance. In addition, as long as at least one receiver of a CE device included in the VPLS instance requests to join a particular multicast group, the PE devices flood the multicast traffic for the multicast group on all ports of the PE devices associated with the VPLS instance.